As known, a distributed power system is gradually used in many electronic devices because of high operating efficiency, high reliability and cost-effectiveness. Since the power loss provided by individual power source of the distributed power system and the heat caused by the distributed power system are both low, the distributed power system is superior to the centralized power system. Since the efficiency for distributing the power by the distributed power system is very high, the adverse effect resulted from the breakdown of the distributed power system is very low, and thus the reliability of the electronic device is enhanced.
For providing more stable voltage conversion, increased powering rating and reduced fabricating cost, the distributed power system is continuously improved. Recently, an intermediate bus power system is provided.
The intermediate bus power system comprises a front-stage voltage-regulating circuit and at least one rear-stage converting circuit. The front-stage voltage-regulating circuit comprises at least one switch element. During operation of the switch element, the input voltage received by the front-stage voltage-regulating circuit is converted into a transition voltage with a fixed value. The rear-stage converting circuit is connected to the front-stage voltage-regulating circuit for receiving the transition voltage and converting the transition voltage into a working voltage required for powering individual load (e.g. 1.8V, 3.3V or 5V). Since the input voltage is converted into the transition voltage by the front-stage voltage-regulating circuit, the transition voltage can be converted into the working voltage by the rear-stage converting circuit without the need of directly converting the input voltage. Under this circumstance, the loss generated during the conversion is performed by the rear-stage converting circuit will be reduced and the rear-stage converting circuit may be implemented by cost-effective components.
For maintaining the transition voltage to be equal to the fixed value, the duty cycle of the switch element is usually adjusted to comply with different levels of the input voltage. For example, if the input voltage is continuously increased, the duty cycle of the switch element of the front-stage voltage-regulating circuit is gradually decreased. Whereas, if the input voltage is continuously decreased, the duty cycle of the switch element of the front-stage voltage-regulating circuit is gradually increased. In other words, by adjusting the duty cycle of the switch element, the input voltage can be converted to the rated voltage value by the front-stage voltage-regulating circuit. However, if the input voltage is too large, the duty cycle of switch element of the front-stage voltage-regulating circuit is adjusted to be very small. Under this circumstance, the front-stage voltage-regulating circuit has increased conduction loss, switching loss and filtering loss, the operating performance is impaired.
Therefore, there is a need of providing an improved front-stage voltage-regulating circuit to obviate the drawbacks encountered from the prior art.